Bmi-1 was originally identified by its over-expression in various leukemias and lymphomas. Subsequently, Bmi-1 has been shown to have oncogenic activity when overexpressed in normal cells and to play a role in the maintenance of cancer stem cell populations. Bmi-1 is elevated in many tumor types and is important in hematologic cancers and many solid tumors, including brain cancers. Reduction of Bmi-1 levels in tumor cells by siRNA causes apoptosis and/or cell senescence and increases susceptibility to cytotoxic agents. Bmi-1 serves as the key regulatory component of the PRC1 complex (polycomb repressive complex-1), but has no enzymatic activity. Therefore, targeting Bmi-1 by traditional drug discovery methods has been problematic.
Since Bmi-1 levels within cells are tightly regulated through both transcriptional and post-transcriptional mechanisms, this regulation can be exploited to target this important protein. Accordingly, there remains a need to provide compounds that inhibit Bmi-1 function and reduce the level of Bmi-1 to treat a cancer mediated by Bmi-1.